Created attachment 247234[details]
testcase, part 2 of 2 (xpcshell script)
Steps to reproduce:
(1) Save the xpcshell script locally.
(2) gdb xpcshell (you need the debugger to get the stack trace) and run
(3) load the script into xpcshell.
(4) runTest();
(5) Wait about ten seconds; the script does do a fetch of the XML document from Bugzilla.

requesting blocking to get opinion from drivers. I don't think it should actually block, but it would be a crasher if an extension hits it (I don't know of any that use LexicalHandler, other than Alex's).

per bz's request, setting in-testsuite? flag. If we create a DOMParser instead of the XMLHttpRequest in the xpcshell script, it should be possible to make this a single-file testcase (JavaScript, xpcshell). Isn't that what our "make check" system likes?